The invention relates to deadbolt locking devices, particularly such devices which supplement the internal locking apparatus furnished with the door. Reference is made to disclosure document number 241240 filed by the inventor on Dec. 19, 1989, in which the concepts of the invention are described.
Deadbolt type locking apparatus are among the most effective and reliable forms of door locks. A typical deadbolt door lock comprises a bolt, which is essentially rectangular and without tapered surfaces, which is in sliding communication with a key turning apparatus on the exterior door side and with a knob on the interior door side. Accordingly, a person inside the door can engage and disengage the deadbolt by turning the knob. A person on the outside of the door however can only engage and disengage the deadbolt by turning it with a key.
An important feature of most deadbolt locking mechanisms is that both the internal knob and the external keyhole apparatus are operably connected in such a manner to the deadbolt that movement of the deadbolt necessarily causes both the knob and the interior keyhole apparatus to move. Accordingly, if the deadbolt is engaged with a key from the outside, this will necessarily result in the interior knob turning with the motion of the deadbolt. If either the knob or the keyhole were further locked so that they could not be moved the deadbolt mechanism could not be moved either and could not be opened from the outside.
Frequently persons who live in apartment complexes or dormitories or the like are provided with deadbolt locks by their landlords. It is not uncommon for all of the deadbolt locks within a given apartment complex or student dormitory to be adapted so as to be engaged with a common master key. Additionally, the landlord may retain a pass key for a particular lock. In such circumstances anyone coming to have possession of the master or pass key would be able to enter any of the units protected by the corresponding deadbolt lock. Additionally, there are those persons who are adept at picking locks open without the required key with "burglar tools". As this may result in the interruption of an individual's privacy or other personal dangers it is helpful to provide some means to prevent the undesired intrusion into such an apartment or school dormitory except with the permission and approval of the inhabitants.
Some prior art devices have been developed which assist in this task. For example U.S. Pat. No. 3,748,882, issued to Dusault, et al, on July 31, 1973, and U.S. Pat. No., 3,423,974, issued to Bernsley, on July 13, 1966, teach apparatus which may be positioned and installed upon a door in order to hold the interior bolt in place. Bernsley teaches a hinged holding member which is adapted with a retaining cavity to fit the interior deadbolt knob. Dusault teaches a pivotally mounted saddle, which may be secured by lugs. The saddle, which must be adapted to fit the given knob, may be pivoted into the locking position and held therein by the legs.
Cook U.S. Pat. No. 4,279,137, issued July 21, 1981, and Brill, U.S. Pat. No. 4,404,826, issued Sept. 20, 1983), are other devices which teach interior locking of deadbolt knobs. They are mentioned only to show the complexity of such devices and the requirement of each that they work with oblong or elliptical shaped interior knobs only. With respect to Suroff (U.S. Pat. No. 3,263,462, issued Aug. 2, 1966) and Cook, supra, it can be seen that some of these devices will only work with knobs at particular orientations.
While a number of such devices have been developed to accomplish this task, there are drawbacks to each of them with respect to either difficulty of installation or means and limitations of operation. Primarily, the limitations of the prior art concern both difficulty and unsightliness of installation as well as the inability of the devices to function with other than an oblong or elliptical knob wherein its length substantially exceeds its width. It would be helpful to provide such a device which is capable of simple installation, foolproof operation, and capability of operation with a variety of interior knobs.